Device for guiding a metal strip on a gas cushion

ABSTRACT

An apparatus is described for guiding a metal band ( 1 ) on a gas cushion with blowing boxes ( 4 ) which are disposed one after the other in the longitudinal direction ( 3 ) of the band and which comprise nozzle fields ( 5 ) which extend transversally to the longitudinal direction ( 3 ) of the band and comprise hole-type nozzles ( 6 ) distributed over the field surface area. In order to provide advantageous constructional conditions it is proposed that the nozzle fields ( 5 ) are provided with a convex basic shape through field sections ( 1, 3 ) which slope in at least one end section at either side transversally to the longitudinal direction of the band.

[0001] An apparatus for guiding a metal band on a gas cushion

[0002] The invention relates to an apparatus for guiding a metal band on a gas cushion with blowing boxes which are disposed one after the other in the longitudinal direction of the band and which comprise nozzle fields which extend transversally to the longitudinal direction of the band and comprise hole-type nozzles distributed over the field surface area.

[0003] In order to enable the conveyance of a metal band floating on a gas cushion in the longitudinal direction of the band it is known (DE 30 26 132 A) to provide blowing boxes which are disposed one after the other in the longitudinal direction of the band and whose nozzle fields extend transversally to the longitudinal direction of the band and comprise hole-type nozzles which are distributed over the field surface area. The gas flowing through said hole-type nozzles against the metal band form a supporting air cushion which is supported by a gas flow from slotted nozzles which extend transversally to the longitudinal direction of the band and delimit the field surface forming the hole-type nozzles. Since the gas cushion is used not only for the contactless guidance of the metal band but also for heat transmission, it is necessary to additionally take the heat influences into account for a heat treatment of the metal band, which lead to the consequence, among other things, that the metal band arches about a central longitudinal axis. This means that the distance of the metal band from the nozzle field is larger than in the zone of the longitudinal edges of the metal band. Due to said arching of the band it is necessary to choose the conditions for the supporting air cushion in such a way that in the middle zone of the metal band a sufficient distance from the blowing boxes must be ensured in order to exclude any contacts in the zone of the longitudinal edges. This necessary increase of the distance in the middle zone leads to a reduction in the carrying force, which then either requires the use of thinner metal bands or an increase in the gas volume flow through the nozzle fields.

[0004] The invention is thus based on the object of providing an apparatus for guiding a metal band on an air cushion of the kind mentioned above in such a way that a metal band arching under the influence of heat can be guided in a contactless manner without having to take into account any loss in carrying force which is caused by the arching of the metal band.

[0005] This object is achieved by the invention in such a way that the nozzle fields are provided with a convex basic shape through field sections which slope in an end section at either side transversally to the longitudinal direction of the band.

[0006] As a result of a convex basic shape of the nozzle fields which is adjusted to the curvature of the metal band, an approximately even distance between the metal band and the nozzle fields can be ensured in a simple manner so that the carrying force of the air cushions as produced by the nozzle fields can be utilized fully without having to fear that the longitudinal edges of the band will touch the blowing boxes. The convex basic shape of the nozzle fields which is adapted to the curvature of the heated metal band further ensures a substantially vertical flow charging of the metal bands in the zone of the longitudinal edge, so that overall favorable carrying conditions can be ensured.

[0007] The continuous progress of the curvature of the metal band transversally to the longitudinal direction of the band can be realized in the simplest case by field sections which slope at either side transversally to the longitudinal direction of the band in an end section of the nozzle fields. In order to ensure a further adjustment of the field surface of the nozzle fields to the curvature of the heated metal band, the field sections of the nozzle fields can increasingly slope at either side. This condition can be achieved by longitudinal sections of the nozzle fields which are combined in a polygon-like way. It is understood that a continuous curvature of the nozzle fields is possible. This requires respectively increased manufacturing efforts, however.

[0008] In the heat treatment of metal bands, blowing boxes with respective nozzle fields are provided both above and below the metal band to be guided in a contactless manner in order to enable an even heat treatment from both sides of the metal band. It is therefore recommended in such a nozzle field arrangement above and below the metal band to be guided to arrange the upper nozzle fields with a concave basic shape which is adapted to the convex basic shape of the lower nozzle fields. Said concave basic shape of the upper nozzle fields naturally does not have any effect on the carrying capacity, but instead has a considerable influence on the even heat transmission, which obviously does not have to be explained in closer detail here.

[0009] The drawing shows the subject matter of the invention in an exemplary fashion. An apparatus in accordance with the invention is shown for guiding a metal band on a gas cushion in sections in a simplified diagram.

[0010] According to the illustrated embodiment, the apparatus for guiding a metal band 1 consists of a frame 2 which carries blowing boxes 4 which are disposed one after the other in the longitudinal direction 3 of the band and which form nozzle fields 5. Said nozzle fields 5 extend transversally to the longitudinal direction 3 of the band and comprise hole-type nozzles 6 which are distributed over the field surface area and through which gas (e.g. air) is blown to form a gas cushion against the metal band 1. Along the edges 7 of the nozzle fields 5 which extend transversally to the longitudinal direction 3 of the band there are slotted nozzles 8 which delimit the field of the hole-type nozzles 6 and which support the gas cushion formed by the hole-type nozzles 6 with their gas jets. The gas flow deflected on the metal band 1 flows off on the one hand between the two rows of slotted nozzles of each nozzle field 5 against the longitudinal edges 9 of the metal band 1 and reaches on the other hand between the return flow channels 10 which are formed between the blowing boxes 4 and which expand with respect to the flow cross section from the longitudinal center of the metal band 1 against the longitudinal edges 9 as a result of the frame surfaces 11 which slope downwardly in a roof-like fashion in order to thus ensure the lowest possible flow speed and thus a comparably low pressure drop.

[0011] In contrast to conventional nozzle fields, the nozzle fields 5 according to the invention are provided with a convex basic shape which is adjusted to the curvature of the heated metal band 1 in order to ensure a distance which remains substantially the same over the band width between the metal band 1 and the nozzle surfaces 5. As can be seen in the illustrated embodiment, the convex basic shape of the blowing boxes 4 is achieved by longitudinal sections 13 of the field surface which start out from a middle section 12 and slope increasingly downwardly and are combined in a polygonal manner in order to enable a sufficient adjustment to the continuous curvature of the curved metal band 1 with simple constructional means. As a result of this adjustment, advantageous carrying conditions are obtained without endangering the contactless guidance of the metal band 1 on the gas cushions of the nozzle fields 5.

[0012] Since an even heat treatment of a metal band 1 from both sides requires nozzle fields on both the lower as well as the upper side of the metal band, the blowing boxes 14 which are disposed above the metal band 1 and are indicated with the dot-dash line can also be provided nozzle fields 5 which are adjusted to the curvature of the metal band 1 and which are then provided with a respective concave basic shape, so that the distance to the metal band 1 can be held approximately similarly over the width of the band.

[0013] It is understood that the invention is not limited to the illustrated embodiment because it is not the type and arrangement of the nozzles that is relevant. Instead, it is merely the convex basic shape of the lower blowing boxes 4 which is adjusted to the curvature of the heated metal band 1 and possibly also the concave basic shape of the nozzle fields 5 of the upper blowing boxes 4 in order to ensure on the one hand advantageous carrying conditions and on the other hand an even heat treatment of the curved metal band 1. 

1. An apparatus for guiding a metal band on a gas cushion with blowing boxes which are disposed one after the other in the longitudinal direction of the band and which comprise nozzle fields which extend transversally to the longitudinal direction of the band and comprise hole-type nozzles distributed over the field surface area, characterized in that the nozzle fields (5) are provided with a convex basic shape through field sections (1, 3) which slope in at least one end section at either side transversally to the longitudinal direction of the band.
 2. An apparatus as claimed in claim 1, characterized in that the field sections (2, 3) of the nozzle fields (5) slope increasingly downwardly to either side.
 3. An apparatus as claimed in claim 1 or 2, characterized in that when providing nozzle fields (5) below and above the metal band (1) to be guided the upper nozzle fields (5) are provided with a concave basic shape which is adjusted to the convex basic shape of the lower nozzle fields (5). 